Various processes useful for rendering polyolefinic polymers flame-proof are already known from the art. These processes are based essentially on the addition to the polymers of thermically unstable halogenated compounds that in the presence of heat decompose to form the corresponding hydrogen halide, i.e., hydrochloric or hydrobromic acid. Examples of such halogenated compounds used in the prior art are: chlorinated paraffin waxes containing from 40% to 75% of chlorine and chlorinated or brominated phenols.
When halogenated compounds of the type of the aforesaid chlorinated paraffin waxes or of the type of the chlorinated or brominated phenols are added to polyethylene or polypropylene, the polymer combustibility undergoes a reduction that depends on the amount of halogen present in the polymer. To achieve a satisfactory degree of uninflammability, however, very high amounts of halogenated compounds, in general higher than 30% by weight with respect to the polymer, are required.
It is also known in the prior art that the amount of halogenated flame-extinguishing additive may be reduced if there is also incorporated in the polymer an oxygenated antimony compond of the type of antimony trioxide or antimony oxyhalides.
Although the antimony trioxide and halogenated paraffin combination yields satisfactory results as far as the self-extinguishing properties they impart to the polymers are concerned, nevertheless, they are not free from rather serious drawbacks. In fact, antimony trioxide must be added to the polymer in amounts higher than 10% by weight and halogenated paraffin in an amount of 15-30% by weight, so that the total additive amount (antimony compound and halogenated paraffin) turns out to be generally comprised between 30% and 35% by weight with respect to the polymer. This causes a strong deterioration of the polymer's mechanical properties (breaking load, yield strength, hardness, resilience), a corrosion of the equipment in which the treatment of materials is carried out, and finally a strong development of toxic smokes and gases in case of fire.